1. Field of the Invention
This invention relates to a new and improved process for preparing organic disulfides from organic sulfonyl halides and mercaptans.
2. Brief Description of the Prior Art
Disulfides are extensively used in the area of polymerization technology. They are used as accelerators in vulcanization, as anti-oxidants and stabilizers for synthetic rubber latexes, as softeners for reclaimed vulcanizates, as intermediates in the manufacture of pigments and insecticides, and as agents for improving the properties of fuel and lubricating oils.
The conventional prior art method for producing organic disulfides involves the oxidation of mercaptans and possesses the disadvantage of requiring expensive and/or hazardous oxidizing agents, such as peroxides or iodine.
Another methd used to prepare disulfides involves reacting a sodium or potassium disulfide with an alkyl halide which has the disadvantage of forming impurities which are difficult to remove. Still another method involves the reaction of highly toxic sulfenyl halides with mercaptans.
Disulfides can also be produced by reduction of organic sulfur-oxygen containing compounds containing sulfur in a higher valence state, such as sulfonyl halide, or thiosulfonates. One such procedure involves th electrochemical reduction of sulfonyl halides, particularly sulfonyl chlorides, to disulfides utilizing a mercury cathode. However, the use of this procedure is not attractive since it tends to lead to mercury pollution of streams and waters and requires expensive equipment and is not well suited to a batch type of process in a plant operation.
Mercaptans, also known as thiols, are known reducing agents in the art for organic sulfur-oxygen containing compounds, as exemplified in Field, JACS 74, 394 (1952) in which aromatic sulfonic acid anhydrides reduced by mercaptans yielding mixtures of thiosulfonates and disulfides.
It is also known in the art that when sulfonyl chlorides are reacted with mercaptans in a ratio of 2 moles of mercaptan per mole of sulfonyl chloride, a mixture of the corresponding sulfinic acid and disulfide is obtained, as exemplified in Gibson, Miller and Smiles, J. Chem. Soc. 127, 1821 (1925). The above reference also discloses that when thiosulfonates (disulphoxides) are reacted with mercaptans in a ratio of 1 mole mercaptan per mole of thiosulfonate, a mixture of sulfinic acid and disulfide is formed. It would appear in light of the prior art that sulfinic acid is a stable by-product in reduction of organic sulfur-oxygen containing compounds using mercaptans.
Thus, the prior art does not provide any process whereby sulfonyl chlorides may be reacted with mercaptans to produce disulfides in high yield and purity, free of by-product sulfinic acid.